A power generation system can include a prime mover that generates electrical power from other primary energy sources. An exemplary prime mover, a gas turbine, is a rotary mechanical device with a gas turbine shaft that drives an electrical generator to supply electrical power to a transmission grid that supplies power to the ultimate users. Another exemplary prime mover is a steam turbine. For fault-free operation, the turbine shaft speed and resulting grid frequency must be maintained within operational ranges. When grid frequency changes abruptly due to a transient event, the turbine controller attempts to restore balance in the power generation system through control of the shaft speed.
A power generation system with a prime mover can include a turbine controller to bring the system back in balance following a transient event on the grid causing a frequency deviation. As an example, when a frequency drop in the grid is detected, a drop in speed of a turbine generator shaft can be detected, for example, because the speed moves with grid frequency. Accordingly, fuel intake by the prime mover may increase based on sensing the drop in speed, which can increase active power output in order to compensate for the drop in frequency. This may result in an increase in the electrical power beyond system limits and, consequently, shut off of fuel to the gas turbine (a condition that can be referred to as flame out). In addition, when a turbine controller tries to react to the fast grid frequency transients, the turbine controller may potentially affect the gas turbine's dynamic behavior. Such a sequence of events may occur because of the turbine controller's reactions to symptoms of the transient event on the grid without recognition of the transient grid event itself. In one embodiment, while a gas turbine is specifically discussed for explanatory purposes, the embodiments described herein apply to any prime mover and are not limited based on the exemplary system.
One challenge in controlling a power generation system (also referred to as a power system herein) is ensuring that the amount of active power consumed (for example, by loads on the power system) in addition to losses in the power system ideally equals the active power produced by the power system. For example, if more power is produced by the power system than consumed by loads and losses, the frequency of the output of the power system can increase. Moreover, deviations from the nominal frequency associated with the power system can damage synchronous machines and other appliances associated with the power system. In one embodiment, circuit breakers, devices that can be reset after they have broken current flow, can be used to control the power flow to various components of the grid and/or power system. In one embodiment, power system can further include switchgears, which can have a combination of electrical disconnect switches, fuses, and/or or circuit breakers to control, protect, and isolate electrical equipment. In another embodiment, switchgears can be used to de-energize equipment to allow work to be done, and to clear faults downstream.
A power system having a gas turbine feedback response mechanism that makes response decisions (for example, making changes to fuel stroke ratio (FSR), fuel splits, fuel bias, a dry low NOx (DLN) mode, or an inlet guide vane (IGV) angle, and the like) based on the speed of the turbine generator shaft alone may have faulty responses. For example, a speed increase in the turbine generator shaft could be a result of system fault or a remote breaker open (RBO) condition. However, a gas turbine feedback response mechanism that only considers feedback based on the speed of the turbine generator shaft may not be able to differentiate between a system fault and a RBO condition.